In cases in which they are used, steering column assemblies or steering columns of the generic type are fitted in a motor vehicle and transfer the torques applied to a steering wheel by the driver into a steering system of the vehicle. Furthermore, in cases in which they are used, steering columns have to withstand various loads, in particular in the event of a collision of the vehicle with an obstacle—the crash case.
DE 10 2005 034 952 B3 discloses for example a steering column which is adjustable in its height and its inclination. A steering spindle is rotatably mounted in an adjusting part, which is also referred to as the casing unit. The casing unit is held in a holding part and the holding part is mounted in a holding clip, which can be fastened to a vehicle body. For adapting the position of the steering spindle, or a steering wheel to be fastened thereto, a clamping system is provided, adjustable by an adjusting lever between an open position and a closed position. In the open position of the clamping system, the casing unit can be displaced in its longitudinal direction with respect to the holding part and at the same time the holding part can be swiveled in its direction of inclination with respect to the holding clip about a swivel axis. In the closed position of the clamping system, the steering spindle is fixed with respect to the holding clip fixed to the body. Such steering columns and clamping systems are known in various embodiments in the prior art.
In a way corresponding to the prior art, the components of such steering columns are made of cast steel, aluminium or magnesium.
There is a general desire for such steering columns to be of a particularly lightweight form. For this purpose, DE 101 55 891 B4 proposes generally making the casing unit (=the central bearing tube) from a thermoplastic or a thermoplastic tube with a glass-fibre or carbon-fibre filling. However, how specifically such a bearing tube may be formed is left open by the disclosure.
EP 0 091 671 B1 discloses a safety steering column, in which a tube part of the steering spindle is formed in one piece with a rigid steering column portion of fibre-reinforced plastic. It is disclosed there that the steering column is produced by a technique of winding around a core, for example of rigid polyurethane foam. In this case, however, the possibilities for the design of the steering column are greatly restricted.
The published patent application DE 102 42 527 A1 discloses a steering column protective housing consisting of a polymer composite material. The steering tube and the mounting brackets are formed by unidirectional strands of fibres that are arranged within a composite material. Mounting brackets may be formed by injection moulding with the use of short fibres, while the steering tube is formed in a compression-moulding process, which includes the use of longer or continuous or oriented fibres. The fibres are usually arranged lying alongside one another and perpendicular to one another or alongside one another and parallel to one another within an adjacent layer of fibres.
DE 198 09 264 A1 discloses a fibrous nonwoven arrangement and a method for producing a preform. In this method, nonwoven layers consisting of unidirectional continuous fibres arranged alongside one another are laid on two-dimensional hotmelt adhesive formations and sewn together with them. Subsequently, to produce the blank for a fibre composite material component, the fibrous nonwoven arrangement is heated, compression-moulded, cooled and demoulded. The preforms produced are then placed into a component thermoforming mould that is not described here, where for example a synthetic resin matrix is fed in and the curing of the composite takes place to form the finished fibre composite material component. The stress profiles in the components can be determined by analytical and numerical methods of calculation. The reinforcing element structure takes these calculations into account, in that the reinforcing fibres are arranged parallel to the stress profiles and the thickness of the component is adapted to the loads. It is precisely at this point that the previously mentioned conventional semifinished fibrous products reach their limits. The reinforcing fibres must lie absolutely parallel to the direction of loading, since only in this way can the full potential of their capability be exploited. Reinforcing fibres should be neither twisted nor undulating in the component, since weak points are thereby implicated. To be able to meet these requirements for the reinforcing element, methods that ensure a defined position of the reinforcing fibres are needed.
The problem addressed by the invention is that of providing a lightweight steering column with which there is a high degree of freedom of design.